A typical computer system includes, among other things, a processor, memory (volatile and non-volatile), and a power supply. The processor runs programs (e.g., an operating system, high-level applications, etc.) which are typically stored in the memory. The power supply powers circuitry within the processor and the memory.
Some computer systems are configured to perform specialized operations. For example, a typical data storage system is a specialized computer system which is configured to perform load and store operations on behalf of one or more external hosts. Such a data storage system can include additional or enhanced computer components for performing the load and storage operations. In particular, some of the volatile memory of a data storage system is typically configured to operate as an input/output (I/O) cache (i.e., cache memory) for temporarily buffering data exchanged between the external hosts and the non-volatile memory (e.g., disk drives).
Some data storage systems include fault tolerant features. For example, one conventional data storage system requires two power supplies to satisfy its entire power needs, but includes three power supplies in the event one of the three power supplies fails. That is, if one of the three power supplies fails, the remaining two power supplies can continue to provide power so that the data storage system remains operational indefinitely, i.e., so that the data storage system can continue storing and retrieving data on behalf of the external hosts. If one of the remaining two power supplies fails, the data storage system cannot continue operating indefinitely and employs a battery backup sub-system for a short period of time in order to shutdown safely without losing any data.
The above-described fault tolerant approach to providing power to a computer system using one more power supply than is overall necessary is called using an N+1 redundancy approach. This approach is appropriately named because it uses the number of power supplies needed to properly power the entire system (N) plus an extra power supply. As such, even if one power supply fails, the system can remain operational.